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Kepware Knowledge Base: Solution

Tags Deactivated and Errors Generated When Editing the PLC Ladder Logic while the Server Is Connected

Last Update: 11/12/2018

Most ladder software will place a PLC in stop or will lock the PLC from processing while ladder logic is being edited. In those situations, error messages will be sent stating that the items being requested do not exist or are unavailable. Users may also get a message stating that the request in invalid. In most cases, the tag will be deactivated and will not be reactivated until the item is requested again (either by removing it from the client and reading it or by stopping and starting the server). To avoid these kinds of errors, it is recommended that users avoid editing the ladder logic on the file in a production system or when data collection is critical.

If users must edit the ladder logic and cannot disconnect the client from the server, they should use the _Enabled system tag to disable data collection during editing and then re-enable it once finished. The _Enabled Tag is a system-level device tag. It is a Boolean tag with a value of 1 when data collection is enabled. To reference it, use the following format: <Channel>.<Device>._System._Enabled. To disable data collection, write a 0. To restart data collection, write a 1.

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